1. Field of the Invention
The present invention relates to a dual band antenna system, more particularly to such an antenna system for use in a portable handheld communication device and which is operable both in an extended and retracted state.
2. Prior Art of the Invention
Portable handheld communication devices, such as a cordless phone, a cellular phone and a PCS (Personal Communications Service) phone, have become increasingly popular. The portable handheld communication devices should be compact and lightweight. It is known to design such a device with a whip antenna that is selectively retracted and extended. The user wishes to keep the device turned on so that a call can be received and the user be notified of such receipt, but at the same time retract the antenna into the case of the device so that the device can be placed in a pocket or purse. Therefore, there is a need for an antenna system operable in dual bands.
A retractable antenna system in accordance with known prior art comprises a 1/4 wavelength whip and a helical antenna placed on top of the whip. The conventional antenna is illustrated in FIGS. 1A and 1B.
Referring to FIG. 1A and 1B, a sleeve 14 is mounted to the upper surface of an case 13. There is a distance between a 1/4 wavelength whip 11 and a 1/4 wavelength helical 12, thereby not affecting each other. This antenna system operates only as a 1/4 wavelength helical antenna when the whip antenna is retracted into the case of the device, and operate only as a 1/4 wavelength whip antenna when the whip antenna is extended out of the case.
When the antenna system is retracted into the case as illustrated in FIG. 1A, only helical section 12 operates. When the antenna system is extended out of the case as illustrated in FIG. 1B, a stopper 15 connected to one end of a whip section 11 is caught in the sleeve 14 and only the whip section 11 operates. The helical antenna 12 is electrically separated from the sleeve 14. This antenna system has problems in that the bandwidth of the helical antenna is narrow and radiation efficiency of the antenna is low. The connection point between the whip 11 and the helical 12 is weak, thereby easily breaking. Also, the antenna uses only single band.